1. Field of the Invention
The present invention relates to a speaker that applies current to a voice coil and thereby vibrates a diaphragm, and more specifically, it relates to a speaker suitable to be installed, for example, in a bumper outside a vehicle cabin.
2. Description of the Related Art
Installing a relatively large speaker, such as a subwoofer for the bass range, in a vehicle cabin reduces the usable space in the vehicle cabin. So, in recent years, a technique has been used in which a speaker is installed inside a member (for example, a bumper) outside a vehicle cabin, and reproduced sound emitted from this speaker is discharged through an opening portion provided in a vehicle cabin wall (body) to the space in the vehicle cabin.
Causing the diaphragm of the speaker to face the opening portion in the vehicle cabin wall when the speaker is installed outside the vehicle cabin enables reproduced sound in the bass range having a high sound pressure to be discharged through the opening portion to the inside of the vehicle cabin without hindrance. However, a member outside the vehicle cabin does not have therein a large storage space like the space in the vehicle cabin, and therefore the diaphragm of the speaker often cannot be caused to face the opening portion in the vehicle cabin wall.
In order to solve this problem, there has been proposed a technique in which a cylindrical duct is provided so as to protrude from the outer peripheral surface of a cone-shaped frame holding the outer periphery of a diaphragm, this duct is inserted into an opening portion in a vehicle cabin wall, and a speaker installed outside a vehicle cabin is caused to communicate with the space in the vehicle cabin through the duct.
As described above, in the related art, an internal space defined by the diaphragm, the damper, and the frame is caused to face an open end of the duct. However, this open end cannot be very large. Therefore, although reproduced sound in the bass range having a high sound pressure is discharged through the duct, high sound quality cannot be expected. In such a conventional speaker, because a cylindrical duct protrudes from the outer peripheral surface of a cone-shaped frame, a duct having a reduced internal diameter at its open end needs to be provided so as to be continuous with the outer peripheral surface of the frame. In order to discharge reproduced sound in the bass range having a high sound pressure at high sound quality, the duct needs to have at least a certain internal diameter. Therefore, when a speaker provided with a duct such as that of the conventional art is a bass speaker such as a subwoofer and is installed outside a vehicle cabin, high sound quality is not obtained. Another special measure needs to be taken.